10-allowing-traffic-with-multiple-selectors.md

ALLOW traffic from apps using multiple selectors

NetworkPolicy lets you define multiple pod selectors to allow traffic from.

Use Case

• Create a combined NetworkPolicy that has the list of microservices that are allowed to connect to an application.

Example

Run a Redis database on your cluster:

kubectl run db --image=redis:4 --port 6379 --expose \
    --labels app=bookstore,role=db

Suppose you would like to share this Redis database between multiple microservices:

service	labels
search	app=bookstore role=search
api	app=bookstore role=api
catalog	app=inventory role=web

The following NetworkPolicy will allow traffic from only these microservices. Save it to redis-allow-services.yaml and apply to the cluster:

kind: NetworkPolicy
apiVersion: networking.k8s.io/v1
metadata:
  name: redis-allow-services
spec:
  podSelector:
    matchLabels:
      app: bookstore
      role: db
  ingress:
  - from:
    - podSelector:
        matchLabels:
          app: bookstore
          role: search
    - podSelector:
        matchLabels:
          app: bookstore
          role: api
    - podSelector:
        matchLabels:
          app: inventory
          role: web

$ kubectl apply -f redis-allow-services.yaml
networkpolicy "redis-allow-services" created

Note that:

• Rules specified in spec.ingress.from are OR'ed.
• This means the pods selected by the selectors are combined are whitelisted altogether.

Try it out

Run a pod that looks like the "catalog" microservice:

$ kubectl run test-$RANDOM --labels=app=inventory,role=web --rm -i -t --image=alpine -- sh

/ # nc -v -w 2 db 6379
db (10.59.242.200:6379) open

(works)

Pods with labels not matching these microservices will not be able to connect:

$ kubectl run test-$RANDOM --labels=app=other --rm -i -t --image=alpine -- sh

/ # nc -v -w 2 db 6379
nc: db (10.59.252.83:6379): Operation timed out

(traffic blocked)

Cleanup

kubectl delete deployment db
kubectl delete service db
kubectl delete networkpolicy redis-allow-services